In football there are sometimes that loses are bound to happen and despite the fact that PSG lost that game go Chelsea doesn't necessarily mean that they will be lose in their game in league 1 because with the quality and standard of that team I don't think any other team can actually challenge them for the league 1 title because they will be winners at the end of the season again and besides lille and Monaco aren't actually big team to give PSG headache.
PSG clearly still reigns supreme in Ligue 1, regardless of what happened to them outside of Ligue 1. PSG's loss in the Club World Cup final against Chelsea is quite commonplace, as Chelsea have been in good form lately, so it's not fair to consider them a weak team. So, what happened to PSG unexpectedly is something they must accept, as they were simply unlucky in that final. However, for next season's Ligue 1, I don't think any other team will be able to stop them from winning the title again and again.